Ice Breaking Android Program

In this tutorial, we will go through the necessary steps you need to take in order to develop your first Android application in Eclipse IDE using the ADT plugin and run it with an Android Virtual Device. We can also use android official IDE Android studio.
The ADT plugin provides easy Android Project creation and management with rich editor features and documentation as well as Android Virtual Device (AVD) management. The workflow on Eclipse and Android studio is similar its depends on you which one you select. we will explain here using Eclipse IDE.

The steps :

1. Download and Install the Android SDK
2. Download and Install the ADT Eclipse plugin
3. Create an Android Virtual Device (AVD)
4. Create an Android Project with Eclipse
5. Run the Application in the Android Virtual Device

Create Android Application

The first step is to create a simple Android Application using Eclipse IDE. Follow the option File -> New -> Project and finally select Android New Application wizard from the wizard list. Now name your application as HelloWorld using the wizard window as follows:

Next, follow the instructions provided and keep all other entries as default till the final step. Once your project is created successfully, you will have following project screen:

Anatomy of Android Application

Before you run your app, you should be aware of a few directories and files in the Android project:

S.N.	Folder, File & Description
1	src This contains the .java source files for your project. By default, it includes an MainActivity.javasource file having an activity class that runs when your app is launched using the app icon.
2	gen This contains the .R file, a compiler-generated file that references all the resources found in your project. You should not modify this file.
3	bin This folder contains the Android package files .apk built by the ADT during the build process and everything else needed to run an Android application.
4	res/drawable-hdpi This is a directory for drawable objects that are designed for high-density screens.
5	res/layout This is a directory for files that define your app's user interface.
6	res/values This is a directory for other various XML files that contain a collection of resources, such as strings and colors definitions.
7	AndroidManifest.xml This is the manifest file which describes the fundamental characteristics of the app and defines each of its components.

The Main Activity File

The main activity code is a Java file MainActivity.java. This is the actual application file which ultimately gets converted to a Dalvik executable and runs your application. Following is the default code generated by the application wizard for Hello World! application:

package com.example.helloworld;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.MenuItem;
import android.support.v4.app.NavUtils;

public class MainActivity extends Activity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.activity_main, menu);
        return true;
    }
}

Here, R.layout.activity_main refers to the activity_main.xml file located in the res/layout folder. TheonCreate() method is one of many methods that are fi red when an activity is loaded.

The Manifest File

Whatever component you develop as a part of your application, you must declare all its components in a manifest file called AndroidManifest.xml which ressides at the root of the application project directory. This file works as an interface between Android OS and your application, so if you do not declare your component in this file, then it will not be considered by the OS. For example, a default manifest file will look like as following file:

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
   package="com.example.helloworld"
   android:versionCode="1"
   android:versionName="1.0" >
   <uses-sdk
      android:minSdkVersion="8"
      android:targetSdkVersion="15" />
   <application
       android:icon="@drawable/ic_launcher"
       android:label="@string/app_name"
       android:theme="@style/AppTheme" >
       <activity
           android:name=".MainActivity"
           android:label="@string/title_activity_main" >
           <intent-filter>
               <action android:name="android.intent.action.MAIN" />
               <category android:name="android.intent.category.LAUNCHER"/>
           </intent-filter>
       </activity>
   </application>
</manifest>